This invention relates to molten carbonate fuel cells and more particularly to materials for the cathode and matrix for molten carbonate fuel cells.
Molten carbonate fuel cells convert the chemical energy of gasifier fuel gases directly into electricity without an intermediate conversion either to heat or to mechanical energy. The electrical chemical fuel cells consist of two porous electrodes separated by an electrolyte contained within a porous matrix. Several hundred single-cell units are generally assembled together to form a molten carbonate fuel cell stack of the size desired.
Prior art anode electrodes for molten carbonate fuel cells were made of nickel or cobalt, for example. Prior art cathode electrodes of these cells were made of silver or nickel, the nickel oxidizing during cell operation providing the catalytic activity of the cathode. However, in catalyzing the reduction of oxygen to accelerate the cathode reaction, the oxidation of the nickel to nickel oxide results in loss of structural integrity of the electrode.
More recently, molten carbonate fuel cells have been proposed which employ a perovskite material as the cathode catalyst. The perovskites are good cathode catalysts for the reduction of oxygen in a molten carbonate electrolyte. One advantage of the use of perovskites is that they are already oxides and therefore do not oxidize during use. Consequently, it is easier to control the structural characteristics which such materials have during operation, particularly as compared to using nickel to form the cathode. However, reactions between the cathode catalyst of molten carbonate fuel cells and other cell compounds tend to limit the usefulness of certain combination catalyst-cell matrix. This is particularly true for lanthanum containing catalysts. For instance, LaNiO.sub.3 reacts with matrix fillers such as LiAlO.sub.2 or Li.sub.2 TiO.sub.3 to form mixed oxides containing La-Al or La-Ti, and the catalyst decomposes to lithiated NiO.